Cooling techniques in solid freeform fabrication

ABSTRACT

A cooling system for removing heat from the layers of a three-dimensional object built in a layerwise manner from a build material in a solid freeform fabrication apparatus. The cooling system provides an air duct that delivers a uniform sheet of air flow over the layers of the three-dimensional object while it is built. It is emphasized that this abstract is provided to comply with the rules requiring an abstract that will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR 1.72(b).

This is a continuation-in-part of U.S. patent application Ser. No.10/000,854 filed on Oct. 24, 2001 entitled “Scanning Techniques inSelective Deposition Modeling.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates in general to solid freeform fabrication and, inparticular, to a cooling technique for removing heat from the surface ofa an object being formed by a solid freeform fabrication apparatus.

2. Description of the Prior Art

Recently, several new technologies have been developed for the rapidcreation of models, prototypes, and parts for limited run manufacturing.These new technologies can generally be described as solid freeformfabrication, herein referred to as “SFF.” Some SFF techniques includestereolithography, selective deposition modeling, laminated objectmanufacturing, selective phase area deposition, multi-phase jetsolidification, ballistic particle manufacturing, fused depositionmodeling, particle deposition, laser sintering, and the like. In SFF,complex parts are produced from a modeling material in an additivefashion as opposed to conventional fabrication techniques, which aregenerally subtractive in nature. For example, in conventionalfabrication techniques material is removed by machining operations orshaped in a die or mold to near net shape and then trimmed. In contrast,additive fabrication techniques incrementally add portions of a buildmaterial to selected locations, typically layer by layer, in order tobuild a complex part.

SFF technologies typically utilize a computer graphic representation ofa part and a supply of a build material to fabricate the part insuccessive layers. SFF technologies have many advantages over the priorconventional manufacturing methods. For instance, SFF technologiesdramatically shorten the time to develop prototype parts and can quicklyproduce limited numbers of parts in rapid manufacturing processes. Theyalso eliminate the need for complex tooling and machining associatedwith the prior conventional manufacturing methods, particularly whencreating molds for casting operations. In addition, SFF technologies areadvantageous because customized objects can be produced quickly byprocessing computer graphic data.

One category of SFF that has emerged is selective deposition modeling,herein referred to as “SDM.” In SDM, a build material is dispensed in alayerwise fashion while in a flowable state and allowed to solidify toform an object. In one type of SDM technology the modeling material isextruded as a continuous filament through a resistively heated nozzle asdescribed, for example, in U.S. Pat. No. 5,303,141 to Batchelder et al.In yet another type of SDM technology the modeling material is jetted ordropped in discrete droplets in order to build up a part. In oneparticular SDM apparatus, a thermoplastic material having a low-meltingpoint is used as the build material, which is delivered through ajetting system such as those used in ink jet printers. One type of SDMprocess utilizing ink jet print heads is described, for example, in U.S.Pat. No. 5,555,176 to Menhennett, et al. Hence, there is a variety ofdispensing devices available for dispensing build material in SDMapplications.

Recently there has developed an interest in dispensing curable phasechange materials in SDM. After dispensing the material, the material iscured by exposure to actinic radiation. This produces a substantialamount of heat that must be removed before dispensing the next layer ofmaterial so that the next layer will solidify. The amount of heat issignificantly greater than that produced when dispensing non-curablematerials. As disclosed in U.S. Pat. No. 6,136,252 to Bedal et al., anaxial fan is used to direct a flow of cooling air over the layers formedfrom a non-curable phase change material. The flow is directedperpendicular to the layers and disperses in all directions along thelayers. Undesirably, this configuration does not produce a uniformdistribution of cooling air across the layers. Further, if flow isincreased to remove the additional heat produced by curable materials,the temperature of the material dispensing device is affected. If thetemperature of the dispensing device is reduced, so too is the drop massof the material being dispensed which can result in build failure.

Thus, there is a need in the art to develop a cooling technique capableof uniformly removing a substantial amount of heat generated in thelayers of the three-dimensional object formed by SFF. These and otherdifficulties have been overcome according to the present invention.

BRIEF SUMMARY OF THE INVENTION

The present invention provides its benefits across a broad spectrum ofSFF processes by providing a method and apparatus for removing heat fromthe layers of a three-dimensional object formed in a layerwise mannerfrom a build material. The cooling system comprises at least one fan forgenerating a flow of air, and at least one air duct in communicationwith the fan for receiving the flow of air. The air duct shapes the flowof air into a uniform sheet of air flow that is delivered from an exitend of the air duct across the layers of the three-dimensional object.The flow is uniform in that the velocity of the air flow issubstantially the same when measured at any location along a transversedirection to the direction of flow at the midpoint of the thickness ofthe sheet of air flow. The air duct is provided with a protrusion on theexit end for diverting the uniform sheet of air flow away from the airduct and towards the layers of the three-dimensional object. In SDMapplications, which dispense a build material from a dispensing device,the protrusion diverts the flow path of the uniform sheet of air flowand has been found to substantially eliminate transient air flows movingtoward the dispensing device.

In some embodiments, the air duct comprises a single containment wallfor shaping the flow of air into a uniform sheet of air flow. In most ofthese single containment wall air duct configurations, the flow of airfrom the fans are bent between the inlet and exit ends of the air ductto bias the air flow against the containment wall as the uniform sheetof air flow is shaped.

In other embodiments, the air duct comprises two containment walls forshaping the flow of air into a uniform sheet of air flow. In most ofthese dual containment wall configurations, two uniform sheets of airflow are delivered across the layers of the three-dimensional object toeffectively double the cooling capacity, when needed.

In most of the embodiments a protrusion is provided upstream from theexit end of the air duct. The sizing of the upstream protrusion adjuststhe thickness of the uniform sheet of air flow and the velocity profileof the thickness of the uniform sheet of air flow. The upstreamprotrusion may or may not be needed depending on the desired airvelocity and cooling rate for a particular application.

A variety of fan configurations are provided for generating the flow ofair that is delivered to the air duct. The fans can be axial fans,centrifugal fans, mixed flow fans, cross flow fans, and the like. Insome embodiments, a plurality of fans are used to generate the air flowused to form the uniform sheet of air flow or multiple uniform sheets ofair flow to cool the three-dimensional object being built.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention method and apparatus will become apparent uponconsideration of the following detailed disclosure of the invention,especially when it is taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a diagrammatic side view of a prior art SDM scanning systemproducing an axial flow of cooling air;

FIG. 2 is a diagrammatic side view of a dispensing trolley of thepresent invention;

FIG. 3 is a diagrammatic side view of another dispensing trolley of thepresent invention;

FIG. 4 is a diagrammatic view of an apparatus for practicing the presentinvention;

FIG. 5 is an isometric diagrammatic view of a curved air duct of thepresent invention;

FIGS. 6A-6I are cross-sectional views of alternative air duct profilesof the present invention;

FIG. 7 is a cross-sectional view of an embodiment of the presentinvention cooling system;

FIG. 8 is an isometric diagrammatic view of the embodiment of FIG. 7;

FIG. 9 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIG. 10 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIG. 11 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIG. 12 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIG. 13 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIG. 14 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIG. 15 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIGS. 16A and 16B are cross-sectional views showing the change inthickness of the uniform sheet of air flow when a protrusion is providedupstream on the air duct;

FIG. 17A and FIG. 17B are respective air velocity profiles of thethickness of the uniform sheet of air flows shown in FIGS. 16A and 16B;

FIG. 18 is a cross-sectional view of another embodiment of the presentinvention cooling system;

FIG. 19 is an isometric diagrammatic view of another embodiment of thepresent is invention cooling system; and

FIG. 20 is an isometric diagrammatic view of an apparatus adapted forpracticing the present invention.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides its benefits across a broad spectrum ofSFF processes. While the description which follows hereinafter is meantto be representative of a number of such applications, it is notexhaustive. As will be understood, the basic apparatus and methodstaught herein can be readily adapted to many uses. It is intended thatthis specification and the claims appended hereto be accorded a breadthin keeping with the scope and spirit of the invention being discloseddespite what might appear to be limiting language imposed by therequirements of referring to the specific examples disclosed.

While the present invention is applicable to all SFF techniques andobjects made therefrom, the invention will be described with respect tosolid deposition modeling utilizing a curable phase change buildmaterial and phase change support material dispensed in a flowablestate. It is to be appreciated that the present invention can beimplemented with any SFF technique utilizing a wide variety ofmaterials. For example, the build material can be a photocurable orsinterable material that is heated to a flowable state but whensolidified may form a high viscosity liquid, a semi-solid, a gel, apaste, or a solid. In addition, the build material may be a compositemixture of components, such as a mixture of photocurable liquid resinand powder material such as metallic, ceramic, or mineral, if desired.In general, the present invention may be implemented with any SFFtechnique where a substantial amount of heat transfer is needed to coolthe object being formed.

As used herein, the term “a flowable state” of a build material is astate wherein the material is unable to resist shear stresses that areinduced by a dispensing device, such as those induced by an ink jetprint head when dispensing the material, causing the material to move orflow. Preferably, the flowable state of the build material is a liquidstate, however, the flowable state of the build material may alsoexhibit thixotropic properties. The term “solidified” and “solidifiable”as used herein refer to the phase change characteristics of a materialwhere the material transitions from the flowable state to a non-flowablestate. A “non-flowable state” of a build material, as used herein, is astate wherein the material is sufficiently self-supportive under its ownweight so as to hold its own shape. A build material existing in a solidstate, a gel state, a paste state, or a thixotropic state, are examplesof a non-flowable state of a build material for the purposes ofdiscussion herein. Further, the term “cured” or “curable” refers to anypolymerization reaction. Preferably the polymerization reaction istriggered by exposure to radiation or thermal heat. Most preferably thepolymerization reaction involves the cross-linking of monomers andoligomers initiated by exposure to actinic radiation in the ultravioletor infrared wavelength band. Further, the term “cured state” refers to amaterial, or portion of a material, in which the polymerization reactionhas substantially completed. It is to be appreciated that as a generalmatter the material can easily transition between the flowable andnon-flowable state prior to being cured, however, once cured, thematerial cannot transition back to a flowable state and be dispensed bythe apparatus.

Additionally, the term “support material” refers to any material that isintended to be dispensed to form a support structure for thethree-dimensional objects as they are being formed, and the term “buildmaterial” refers to any material that is intended to be dispensed toform the three-dimensional objects. The build material and the supportmaterial may be similar materials having similar formulations but, forpurposes herein, they are to be distinguished only by their intendeduse.

Furthermore, the term “main scanning direction” refers to the directionof the reciprocal back and forth motion necessary to dispense materialto form three-dimensional objects. The three-dimensional objects areformed by dispensing the materials to specific drop locations on rasteror scanning lines aligned in the main scanning direction within thebuild environment. Generally, each raster line is associated with adischarge orifice of the dispensing device. With reference to thefigures, the main scanning direction is the direction of the X-axis ofthe Cartesian coordinate system shown. The term “secondary scanningdirection” refers to the sideways motion necessary to offset the rasterlines associated with the discharge orifices of the dispensing devicerelative to the object being formed so the discharge orifices do notdispense along just one path on the object. With reference to thefigures, the secondary scanning direction is the direction along theY-axis of the Cartesian coordinate system shown. The term “builddirection” refers to a direction that is perpendicular to the layersbeing formed by an SDM apparatus. The apparatus must shift thedispensing device relative to the object staging structure in the builddirection as the layers are formed during the build process. Withreference to the figures the shift in the build direction is thedirection along the Z-axis of the Cartesian coordinate system shown.Further, a “substantially stationary” dispensing device refers to adispensing device in an apparatus that does not move relative to theapparatus when dispensing material in the mains scanning direction, butmay move in the secondary scanning direction and build direction whennot dispensing material. The term “object staging structure” refers toany structure capable of supporting a three-dimensional object as it isformed in a layerwise manner by an SDM apparatus. For example, a plateor build platform can be used as an object staging structure, as well asa mesh grating or container, if desired.

In addition, the term a “uniform sheet of air flow” refers to anelongated stream of air flowing in a one direction along a surface suchas a layer of a three-dimensional object being formed by any SFFprocess. The flow is uniform in that the velocity of the air flow issubstantially the same when measured at any location along a transversedirection to the direction of flow at the midpoint of the thickness ofthe sheet of air flow. The velocity of the air flow measured in atransverse direction to the direction of flow along the midpoint of thethickness of the sheet should not vary by more than about 35%, and morepreferably by no more than about 10%. Most preferably the velocity ofthe air flow within the sheet does not vary at all. Since the velocityof the air flow is directly related to the cooling rate of the surfaceover which it passes, the uniform sheet of air flow provided over thelayers of a three-dimensional object formed by SFF helps achieve moreconsistent cooling for the object.

A conventional SDM scanning methodology is shown in FIG. 1. Generally,the dispensing trolley 11 carries the dispensing device 13, planarizer15, and cooling fans 17, and is reciprocally driven in the main scanningdirection 12 between opposed ends 14 in the build environment 25. Thecooling fans 17 direct a cooling stream of air in a directionperpendicular to the layers being formed. Upon contact with the layersthe cooling stream spreads out in all directions across the layers. Thebuild platform 19 is offset in the secondary scanning direction 16 forrandomizing dispensing and for targeting all locations parallel to themain scanning direction. The secondary scanning direction 16 isrepresented as a circle and dot in FIG. 1 since it is coincident withthe line of sight of that view. The build platform 19 is also shifted inthe build direction after each layer is formed. The SDM computercontroller or processor 21 coordinates these motions and provides thefiring pulses to the dispensing orifices 23 to dispense the material ontargeted drop locations on the scanning lines. This conventionalscanning technique is discussed, for example, in U.S. Pat. No. 6,136,252to Bedal et al.

Now, referring to FIG. 2, a preferred scanning methodology is shown. Thebuild platform 19 is reciprocally driven in the main scanning direction12 between opposed ends 14 in the build environment 25, instead of thedispensing trolley 11. The dispensing trolley 11 remains substantiallystationary during motion in the main scanning direction. The dispensingtrolley is offset in the secondary scanning direction 16 forrandomization when the build platform is at the opposed ends 14 of thereciprocating motion in the main scanning direction, and is shiftedupward in the build direction after each layer is formed. Alternatively,the build platform may be offset in the secondary scanning direction 16and shifted downward in the build direction 18, if desired.

Referring to FIG. 2 a flow of air 22 for cooling the object is providedon the dispensing trolley 11. Since a preferred build material iscurable by exposure to actinic radiation, a significant amount of heatis generated during the layer formation process. This heat, in additionto the latent heat generated from the material as it transitions into anon-flowable state, must be removed without affecting the temperature ofthe dispensing device. The conventional cooling fan configuration shownin FIG. 1 provides an air profile in the shape of an inverted “T” thatmoves vertically downward towards the object and then disperses in alldirections over the surface of the object. The inverted “T” air profileis sufficient for cooling objects in the prior SDM systems dispensingnon-curable materials. However, increasing the air velocity of theinverted “T” air profile to meet the cooling capacity needed for curablematerials undesirably affects the dispensing temperature of dispensingdevices such as ink jet print heads used in SDM. As the dispensingtemperature drops, so to does the drop mass of the dispensed material.Thus, non-uniform temperature distributions around the print head createnon-uniform drop mass of ejected material droplets across the print headarray. In addition, prior scanning techniques that reciprocate the printhead throughout the build environment also contribute to this problem.

In order to maintain a uniform dispensing temperature across thedispensing device 13 it is desirable to substantially eliminate thetransient convection air flows occurring around the print head whilealso providing the necessary cooling air flow rates required forremoving heat from the layers of the object being formed. Referring toFIG. 2, a flow of air 22 for cooling the object is provided on thedispensing trolley 11. The flow of air 22 is directed away from thedispensing device 13 in the shape of a uniform sheet of air flow 94 overthe surface of the object 20 being formed below. Cooling air enters afan or blower 24 as indicated by arrow 26. In the embodiment shown, thefan 24 is a centrifugal fan that is elongated and extends the entirelength of the dispensing device 13 in the Y-direction, which iscoincident with the line of sight of FIG. 2. Alternatively, the fan maybe an axial fan, a mixed flow fan, a cross flow fan, or the like. Thefan or blower 24 ejects the air outwardly in a horizontal manner as asheet of air shown by numeral 92 towards a curved air duct 28 whichre-directs the sheet of air vertically downward toward the object 20being formed. The flow of air 92 is shaped into a substantially uniformsheet of air 94 so that uniform cooling can be provided by convectionacross the surface of the layers. A protrusion 30 is provided toinitially trip the flow of air to thicken the width of the sheet asshown at 32, which in turn thickens the width of the sheet in the areaindicated by numeral 22. At the exit end of the air duct 28 there isanother protrusion 34. The protrusions 34 and 30 establish high pressurezones 36, which impart a sideways force on the stream of air thatdiverts the stream air flow away from the dispensing device 13. Thediverted flow path of the sheet of air is shown by numeral 22. The pointwhere the uniform sheet of air flow 94 traverses the surface of theobject 20 is shown by numeral 38. Heat is transferred by convection fromthe object 20 to the air flow, which travels away from the object anddispensing device in the direction noted by numeral 40. The uniformsheet of air flow 94 is directed away from the dispensing device 13 tosubstantially prevent active cooling of the dispensing device 13. Thisis true even when the air flow does not traverse the object 20, such aswhen the build platform 15 is located at the left opposed end 22 in FIG.8. However, as the build platform 15 moves from right to left, theuniform sheet of air flow 94 is directed across the surface 38 of theobject 20.

The protrusion 34, which diverts the flow path of the uniform sheet ofair flow, has been found to substantially eliminate transient air flowmoving toward the dispensing device. Experiments were conducted whereina flow of air from a flat air duct was provided at an inclined angle tothe object surface in order to eliminate transient air flow movingbackwards toward the dispensing device. The inclined angle was intendedto direct the air flow away from the dispensing device. However, theseexperiments revealed that transient air flow still migrated backwards tothe dispensing device, and could not be substantially eliminated. Thus,it is believed that the provision of the protrusion on the exit end ofthe air duct to divert the uniform sheet of air flow prevents transientair flow from migrating toward the dispensing device.

With the uniform sheet of air flow being directed away from thedispensing device 13, the velocity of the air flow can be substantiallyincreased in order to achieve the desired heat transfer rate necessaryfor removing the heat being released from the layers ofthree-dimensional object. In addition, with the print head positionedbetween the uniform sheet of air flow 94 and the planarizer 15, a pocketof air 42 is established around the dispensing device 13. This pocket orbuffer zone of air 42 is substantially undisturbed within the apparatusand provides an insulating or shielding effect around the dispensingdevice 13. This in turn allows for more uniform temperature control ofthe dispensing device.

The dispensing trolley 11 in FIG. 2 shows just one uniform sheet of airflow 94 for cooling the object 20. In the embodiment shown in FIG. 3, asecond uniform sheet of air flow 94′ for cooling the object is providedadjacent to the planarizer 15 on the left side of the dispensing trolley11. The second uniform sheet of air flow 94′ is the mirror image of theone shown in FIG. 2 and has its own fan 24′ for generating the air flow.The second uniform sheet of air flow 94′ is diverted outwardly to theleft. Utilizing two uniform sheets of air flows effectively doubles theconvention heat transfer capabilities of the system. This configurationis desirable when just one uniform sheet of air flow is insufficient toremove the heat from the layers of the object 20 formed within the SDMapparatus. Furthermore it is to be appreciated that the configuration ofthe uniform sheets of air flows may also be implemented on thedispensing device 11 of the prior art scanning methodology shown in FIG.1, if desired.

Referring to FIG. 4 there is illustrated generally by the numeral 10 asolid freeform fabrication apparatus for practicing the presentinvention. The build platform 19 is reciprocally driven by theconventional drive means and motor 44, instead of the dispensing trolley11 shown in FIG. 1. A gear reduction means 46 is provided so that themotor 44 can be driven at a high speed under low torque conditions. Thiseliminates the control problems associated with accelerating anddecelerating a varying mass. The dispensing trolley 11 is preciselypositioned by actuation means 48 in the build direction to adjust foreach layer of the object 20 as it is formed. The actuation means 48comprises precision lead screw linear actuators driven by servomotors(both not shown). The ends of the linear actuators of the actuationmeans 48 reside on opposite ends of the build environment 25 and in atransverse direction to the direction of reciprocation of the buildplatform. In this transverse direction, which is in line with thesecondary scanning direction 16, the dispensing trolley 11 is shifted toexecute randomization as discussed previously. However, for ease ofillustration in FIG. 4, the linear actuators and dispensing trolley areshown in a two-dimensionally flat manner giving the appearance that thelinear actuators are aligned in the direction of reciprocation of thebuild platform 19. Although they may be aligned with the direction ofreciprocation, the use of space within the apparatus is optimized bysituating them in a transverse direction to the reciprocation in themain scanning direction.

In the build environment generally illustrated by numeral 25, there isshown by numeral 20 a three-dimensional object being formed withintegrally formed supports 50. The object 20 and supports 50 both residein a sufficiently fixed manner on the build platform 15 so as towithstand the acceleration and deceleration forces induced duringreciprocation of the build platform while still being removable from theplatform. This is achieved by dispensing at least one layer of supportmaterial on the build platform before dispensing the build materialsince the support material is designed to be removed at the end of thebuild process. The material identified by numeral 52A is dispensed bythe apparatus 10 to form the three-dimensional object 20, and thematerial identified by numeral 52B is dispensed to form the support 50.Containers identified generally by numerals 54A and 54B respectivelyhold a discrete amount of these two materials 52A and 52B. Umbilicals56A and 56B respectively deliver the material to the dispensing device13, which in the embodiment shown is an ink jet print head having aplurality of dispensing orifices 23.

The dispensing trolley 11 shown in FIG. 4 comprises a heated planarizer15 that removes excess material from the layers to normalize the layersbeing dispensed. The heated planarizer 15 contacts the material in anon-flowable state and because it is heated, locally transforms some ofthe material to a flowable state. Due to the forces of surface tension,this excess flowable material adheres to the surface of the planarizer,and as the planarizer rotates the material is brought up to the skive 58which is in contact with the planarizer 15. The skive 58 separates thematerial from the surface of the planarizer 15 and directs the flowablematerial into a waste reservoir identified generally by numeral 60located on the trolley 11. A heater 62 and thermistor 64 on the wastereservoir 60 operate to maintain the temperature of the waste reservoirat a sufficient level so that the waste material in the reservoirremains in the flowable state. The dispensing trolley 11 is configuredto have two uniform sheets of air flows for cooling the object as shownin FIG. 3, however the air flows have been omitted in FIG. 4 for ease ofillustration.

In the apparatus shown in FIG. 4, the build material 52A is a phasechange material that is cured by exposure to actinic radiation. Afterthe curable phase change material 52A is dispensed in a layer ittransitions from the flowable state to a non-flowable state. After alayer has been normalized by the passage of the planarizer 15 over thelayer, the layer is then exposed to actinic radiation by radiationsource 66. Preferably the actinic radiation is in the ultraviolet orinfrared band of the spectrum. For this SDM apparatus, planarizingoccurs prior to exposing a layer to the radiation source 66. This isbecause the planarizer shown can only normalize the layers if thematerial in the layers can be changed from the non-flowable to theflowable state, which cannot occur if the material 52A has been alreadycured by exposure to radiation. However, the planarizer may be replacedwith a mill cutter or similar device that chips or grinds the layerssmooth, which could normalize the layers even after they have beencured, if desired.

In conjunction with the curable build material 52A, a non-curable phasechange material 52B is used for forming the support 50. Since thesupport material cannot be cured, it can be removed from the object andbuild platform, for example, by being dissolved in a solvent or by beingmelted by application of heat. A preferred method for removing thesupport material is disclosed in U.S. patent application Ser. No.09/970,727 filed Oct. 3, 2001 entitled “Post ProcessingThree-Dimensional Objects Formed by Selective Deposition Modeling”, nowU.S. Pat. No. 6,752,948. A preferred method for dispensing a curablephase change material to form a three-dimensional object and fordispensing a non-curable phase change material to form supports for theobject is disclosed in U.S. patent application Ser. No. 09/971,337 filedOct. 3, 2001 entitled “Selective Deposition Modeling with Curable PhaseChange Materials.” A preferred curable phase change material andnon-curable phase change support material is disclosed in U.S. patentapplication Ser. No. 09/971,247 filed Oct. 3, 2001 entitled“Ultra-Violet Light Curable Hot Melt Composition.” A preferred materialfeed and waste is disclosed in U.S. patent application Ser. No.09/970,956, filed Oct. 3, 2001 entitled “Quantized Feed System.” All ofthese related applications are incorporated by reference in theirentirety herein.

The air duct 28 is shown in further detail in FIG. 5. The air duct 28has an inlet end identified generally by numeral 68 and exit endidentified generally by numeral 70. The air duct has guide walls 72extending between the inlet end and exit end which constrain the flow ofair traveling through the air duct to prevent the flow of air fromfanning out as the air exits from the air duct 28. The air duct 28 shownin FIG. 5 forms a single containment wall that is curved so as to bendthe air flow approximately 90 degrees as it travels from the inlet endto the exit end. Because the curvilinear motion of the air flow impartsa centrifugal force that acts against the air duct 28, the air flow isbiased against the air duct as it travels from the inlet end 68 to theexit end 70. Hence, the air duct configuration shown in FIG. 5 does notneed an additional containment wall to form the uniform sheet of airflow.

It is not necessary for the air duct comprising a single containmentwall to bend the air 90 degrees as it travels from the inlet end to theexit end of the duct to establish the uniform sheet of air flow.Referring to FIG. 18, the bend angle of the air duct 28, identified bynumeral 108, can be significantly less than 90 degrees, such as about 10degrees or less, if desired. In addition, the bend angle can be greaterthan 90 degrees, such as up to 180 degrees, if desired. Whatever bendangle 108 is used, a large bend radius 110 along the containment wallwill provide for a uniform sheet of air flow traveling along the surfaceof the air duct between the inlet and exit ends. The large bend radiusfurther assists the shaping of the uniform sheet of air flow for coolingthe layers of the object being formed. However, the air duct may also besubstantially straight as long as the air duct is provided with auniform sheet of air flow directly from the fan or fans that generatethe air flow.

In FIG. 5 the protrusion 34 which establishes the high pressure zone 36to divert the air flow is square in cross-section, however otherconfigurations may be used as well. Referring to FIGS. 6A through 6I anumber of alternative configurations for the shape of the protrusion 34are shown. In FIG. 6A, the protrusion 34 is square in cross section asin FIG. 5. In FIG. 6B, a double step configuration is shown while inFIG. 6C the protrusion 34 is a tab extending generally perpendicular atthe end of the air duct 28. Still further, FIGS. 6D, 6E, and 6I showalternative configurations incorporating either a convex or concaveradius on the protrusion 34. In FIG. 6F a chamfered configuration isshown and in FIG. 6H a reverse chamfer configuration is shown. In FIG.6G a double sided tab configuration is shown. Other configurations andcombinations of shapes for the protrusion are possible as well, such aspolygonal shapes, elliptical shapes, and the like.

Another embodiment of the present invention cooling system is shown inFIGS. 7 and 8. The air duct 28 in this embodiment is the same as the oneshown in FIG. 5, however a plurality of fans 24 are used. The fans 24are arrayed above a cowling 74 which directs the air 26 drawn throughthe fans 24 towards the air duct 28 through opening 76. In thisembodiment the fans 24 are axial fans used in conjunction with thecowling 74 to generate the flow of air delivered to the air duct 28,instead of the elongated centrifugal fan configuration shown in FIGS. 2and 3. The cowling may include guide vanes (not shown) to direct theflow of air in a single direction towards the air duct 28. Further,guide vanes may also be provided on the air duct 28, if needed. It mayalso be desirable to stagger the direction of rotation of the fans, forexample, by rotating one fan clockwise and an adjacent fan counterclockwise so as to minimize spiraling effects in the air flow stream.

Another embodiment of the present invention cooling system is shown inFIG. 9. In this embodiment two arrays of axial fans 24 generate the flowof air that is delivered to the air duct 28 through a cowling 74. Twoseparate openings draw in the air 26 to form the air flow. Anotherembodiment having a double array of axial fans 24 is shown in FIG. 10where the cowling 74 positions the fans 24 at an angle as opposed to theparallel configuration shown in FIG. 9.

Another embodiment of the present invention cooling system is shown inFIG. 11 in conjunction with a dispensing trolley 11 carrying adispensing device 13 and planarizer 15. In this embodiment, the air ductcomprises a first containment wall 78 and second containment wall 80which function to form two uniform sheets of air flows similar to thoseshown in FIG. 3. However, in this embodiment an array of axial fans 24is provided to generate a flow of air that is divided in two to form twouniform sheets of air flow. Further, the protrusion 30 that widens thethickness of the uniform sheets of air flow is located on the firstguide wall and the protrusion 34 that diverts the sheets away from thedispensing device is located on the ends of the second guide wall 80.Four embodiments similar to the one shown in FIG. 11 are shown in FIGS.12, 13, 14, and 15. These embodiments possess a similar air ductstructure, however, they employ different fan configurations forgenerating the air flow. In FIG. 12, a double stacked array of axialfans 24 are used to generate the air flow needed to form the uniformssheets of air flows. In the embodiment shown in FIG. 13, two separatearrays of axial fans 24 are used to generate the air flow needed. InFIG. 14 a centrifugal fan 24 is used having an axial air inlet 26 thatis coincident with the line of sight in the view. Further, theembodiment shown in FIG. 15 comprises two elongated centrifugal fans 24for generating the air flow needed. When centrifugal fans are used, theycan have straight radial blades, curved forward blades, curved backwardblades, or straight backward blades. In addition, other fan types can beused as well, such as mixed flow fans and cross flow fans, if desired.

It is to be appreciated that when forming the air duct with twocontainment walls, the flow of air need not be bent as it travels fromthe inlet end to the exit end of the air duct when forming the uniformsheet of air flow. Hence, the containment walls may be substantiallystraight instead of being curved, as are shown in the air ductconfigurations in FIGS. 11, 12, 13, 14, and 15.

Now referring to FIGS. 16A, 16B, and 17A, 17B the effect on thethickness of the uniform sheet of air flow by the provision of theprotrusion 30 is shown. FIG. 16A shows air duct 28 without theprotrusion upstream from the exit end of the air duct. Without theupstream protrusion, the thickness 82 for the uniform sheet of air flowadjacent protrusion 34 is established as shown. The velocity profile ofthe sheet of air flow taken at thickness 82 is shown in FIG. 17A bynumeral 100. The same air duct is shown including the protrusion 30upstream from the exit end of the air duct 28 is shown in FIG. 16B. Asdiscussed in conjunction with FIG. 2, the protrusion 30 triggers the airflow to widen just after the protrusion, as indicated by numeral 32. Thewidening of the air flow caused by the protrusion 30 also widens thethickness 84 of the uniform sheet of air flow adjacent the protrusion 34compared to the thickness 82 of the air flow without the protrusion. Thevelocity profile of the sheet of air flow taken along the thickness 84is shown in FIG. 17A by numeral 102. As shown in FIGS. 17A and 17B, thevelocity profile is more uniform across the thickness of the sheet ofair flow when the upstream protrusion is provided. Further, the peak airvelocity of the profile, identified by numeral 104 in FIG. 17B and bynumeral 106 in FIG. 17A, is less when the upstream protrusion isprovided on the air duct. Normally the peak air velocity of the profilewill reside generally at the midpoint of the thickness of the sheet ofair flow. According to the present invention, the peak air velocityremains substantially the same when measured at any location along atransverse direction to the direction of flow. However, lowering thepeak air velocity of the profile may be needed in order to preventdamage to the object being formed, and particularly when forminggeometrically fragile objects under optimal cooling rates. Thus, theprotrusion 30 can be used to optimally adjust the thickness of theuniform sheet of air flow and the velocity profile of the thickness ofthe uniform sheet of air flow as may be needed depending on the desiredair velocity and cooling rate for a particular application. However, notall applications will need the upstream protrusion according to thepresent invention.

Referring to FIG. 19 another alternative embodiment of the presentinvention cooling system is shown. In this embodiment two separateuniform sheets of air flow are provided which are directed substantiallyparallel to the secondary scanning direction 16. The two cooling systemsrepresented by air ducts 28 and centrifugal fans 24 need not be mountedon the dispensing trolley with the dispensing device 13 and planarizer15 as in the other embodiments.

Now referring to FIG. 20, an SDM apparatus is shown at 10 for practicingthe present invention. To access the build environment, a slideable door86 is provided at the front of the apparatus. The object can be easilyremoved when the build platform (not shown) is positioned at the opposedend of reciprocation adjacent slideable door 86. The door 86 does notallow radiation within the machine to escape into the environment. Theapparatus is configured such that it will not operate or turn on whenthe door 86 open. In addition, when the apparatus is in operation thedoor 86 will not open. A build material feed door 88 is provided so thatthe build material can be inserted into the apparatus 10. A supportmaterial feed door 70 is also provided so that the support material canbe inserted into the apparatus 10. A waste drawer 90 is provided at thebottom end of the apparatus 10 so that the expelled waste containers canbe removed from the apparatus. A user interface 98 is provided which isin communication with the external computer 35 previously discussedwhich tracks receipt of the print command data from an externalcomputer.

What have been described are preferred embodiments in whichmodifications and changes may be made without departing from the spiritand scope of the accompanying claims.

1. A method of forming a three-dimensional object in a layerwise mannerfrom a build material, the method comprising: providing object layerdata; forming layers of the three-dimensional object according to theobject layer data; and providing at least one substantially uniformsheet of air flow across the layers of the three-dimensional object toremove heat from the layers of the three-dimensional object, the uniformsheet of air flow being established by directing a flow of air along anair duct, the air duct having a protrusion diverting the air flow awayfrom the air duct and towards the layers of the three-dimensionalobject.
 2. The method of claim 1 further comprising: forming the layersof the three-dimensional object by dispensing the build material from adispensing device; and directing the uniform sheet of air flow away fromthe dispensing device.
 3. The method of claim 2 further comprising:establishing reciprocal motion in a main scanning direction relativelybetween the three-dimensional object and the dispensing device; andwherein the substantially uniform sheet of air flow is directedsubstantially parallel to the main scanning direction.
 4. The method ofclaim 2 further comprising: establishing motion in a secondary scanningdirection relatively between the three-dimensional object and thedispensing device; and wherein the substantially uniform sheet of airflow is directed substantially parallel to the secondary scanningdirection.
 5. The method of claim 2 further comprising: establishing asubstantially undisturbed pocket of air around the dispensing device bydirecting the air flow away from the dispensing device.
 6. A method offorming a three-dimensional object in a layerwise manner from a buildmaterial, the method comprising: providing object layer data; forminglayers of the three-dimensional object according to the object layerdata; and providing at least two substantially uniform sheets of airflow across the layers or the three-dimensional object wherein theuniform sheets of air flow are established by directing a flow of airalong a air duct having an inlet end and exit end, the air duct having aprotrusion on the exit end, the protrusion diverting the flow of airaway from the air duct and toward the layers of the three-dimensionalobject.
 7. The method of claim 6 further comprising: forming the layersof the three-dimensional object by dispensing the build material from adispensing device; and establishing a substantially undisturbed pocketof air around the dispensing device by positioning the substantiallyuniform sheets of air flow on opposed sides of the dispensing device anddiverting each sheet of air flow away from the dispensing device.
 8. Themethod of claim 7 further comprising: establishing reciprocal motion ina main scanning direction relatively the three-dimensional object andthe dispensing device; and wherein the substantially uniform sheets ofair flow are directed in opposite directions that are substantiallyparallel to the main scanning direction.
 9. The method of claim 7further comprising: establishing motion in a secondary scanningdirection relatively between the three-dimensional object and thedispensing device; and wherein the substantially uniform sheets of airflow are directed substantially parallel to the secondary scanningdirection.
 10. A method of forming a three-dimensional object in alayerwise manner from a build material, the method comprising: providingobject layer data; forming layers of the three-dimensional objectaccording to the object layer data; providing at least one substantiallyuniform sheet of air flow across the layers of the three-dimensionalobject to remove heat from the layers of the three-dimensional object,the at least one uniform sheet of air flow being redirected by a curvedducting and at least one protrusion to thicken the width of the uniformsheet of air flow and direct it towards the layers of thethree-dimensional object.
 11. The method of claim 10 further comprising:forming the layers of the three-dimensional object by dispensing thebuild material from a dispensing device; and directing the uniform sheetof air flow away from the dispensing device.
 12. The method of claim 11further comprising: establishing reciprocal motion in a main scanningdirection relatively between the three-dimensional object and thedispensing device; and wherein the substantially uniform sheet of airhow is directed substantially parallel to the main scanning direction.13. The method of claim 11 further comprising: establishing motion in asecondary scanning direction relatively between the three-dimensionalobject and the dispensing device; and wherein the substantially uniformsheet of air flow is directed substantially parallel to the secondaryscanning direction.
 14. The method of claim 11 further comprising:establishing a substantially undisturbed pocket of air around thedispensing device by directing the air flow away from the dispensingdevice.